Cycle 4 and 5 Scheduling
For Cycles 4 and 5 we introduced
an additional component of the scheduling process:
scheduling priorities. When the cryogen runs out we want to make sure that the
highest priority science selected in the review process has been executed. In Cycles 1 and
2, observations were scheduled to create the most efficient schedule possible without
explicitly attempting to schedule the highest ranked science programs first. Large
programs and those with tight timing constraints therefore drove the layout of the basic
instrument campaigns. In Cycle-3 we began implementing scheduling priorities for the
small programs based on the science ranking from the review process. For observations
selected in Cycles 1-3 we have effectively promised to execute every observation
selected. Observations from previous cycles were given the highest priority if not
executed before the end of the cycle. Starting with observations selected in Cycle-4 we
can no longer expect to execute every observation selected in the cycle.
Cycle-4 Scheduling
All observations selected in Cycle-4 will be assigned an explicit scheduling priority
(1, 2, 3). For the GO programs, one-third of the selected hours will be assigned to each
priority based on the science ranking from the Cycle-4 review. During the first six
months of the cycle, we expect to primarily schedule observations with priority 1 and 2.
In general, priority 3 observations will be scheduled if nothing in the higher priority bins
can be scheduled. The majority of priority 3 observations will not move into the
scheduling pool until early 2008.
The GTO programs selected in Cycle-4 will also be
assigned scheduling priorities. For each GTO team, one-third of
their selected program will be assigned to each priority bin based on the science ranking
in the Cycle-4 review. These will be scheduled in the same way as the GO programs.
Observations with scheduling priority 3 with tight timing constraints may be very
difficult to schedule. All observations eligible for funding in Cycle-4 will be funded
without regard to scheduling priority.
Cycle-4/5 Scheduling Transition
All observations selected in Cycle-4 will be not executed by the end of the Cycle.
The observations remaining in the pool at the end of Cycle-4 will mostly be those with
priority 3. When the Cycle-5 program is selected, observations from Cycle-4 will not
immediately be given top priority for scheduling but they will be moved up one priority
level. For example, Cycle-4 observations with priority 3 will be given priority 2 in
Cycle-5.
Cycle-5 Scheduling
Cycle-5 is the last cryogenic cycle. We expect it to last 8-10 months but will select an
entire year of observations at the Cycle-5 review. Observations will again be assigned
scheduling priorities. 25% of the selected Cycle-5 observations will be assigned priority
1, 25% will be assigned priority 2 and 50% will be assigned priority 3. We will make
every effort to schedule all priority 1 observations. Priority 2 observations will also be
placed immediately into the scheduling pool. Observations with priority 3 will not enter
the scheduling pool until 6 months into the cycle or until nothing else is available for
scheduling. We will accept a slight decrease in scheduling efficiency (<5%) to ensure that
the highest priority science is executed first.
Completion of programs that are started will
be our goal. We will fund eligible priority 1 and 2 observations at the beginning of
Cycle-5. Observations with priority 3 will be not funded until the program begins
execution.
Long Range Planning
After each proposal call, a major adjustment to the long range planning is
made. The end products of the episodic long range planning activity are a
Baseline Instrument
Campaign (BIC) plan, which provides an outline structure for the order
and length of each instrument campaign and a set of plan windows for each
observation. Highly constrained activities and conflicts are also
identified at this point in the process. Once a BIC is established,
incremental changes may be made to it as scheduling proceeds, in order to
deal with such issues as DSN station allocations and constraints imposed
by the previous week's schedule.
The BIC is developed by the Observatory Planning and Scheduling Team
(OPST) based upon three things: 1) the optimal ordering of the instruments
(IRAC-MIPS-IRS), 2) the optimal length of an instrument campaign (5-14 days)
and, 3) the number of hours of observing time on each instrument in the
science operations database (about 9:8:6 prior to Cycle-1, about
8:13:14 during Cycle-1, about 10:12:12 during Cycle-2, and
about 7:12:16 for Cycle-3).
Starting with this very basic structure, the
OPST adjusts the lengths and boundaries to accommodate any highly
constrained activities or heavily subscribed periods.
Plan windows for Spitzer consist of the intersection between instrument
availability per the BIC, visibility constraints and any timing
constraints which have been placed. They allow OPST to identify which
observations are available to schedule in a given time period, but
do not represent a commitment to schedule the observation in any
particular window.
Scheduling
Scheduling begins about 5 weeks prior to when a sequence begins execution
on the observatory. Since the sequences run from Wednesday to Wednesday,
this process usually begins on the Monday of the 5th week in advance, but
can be slightly earlier on any given week.
The scheduling process consists of laying down spacecraft and science
instrument calibrations, selecting a "pool" of available science
observations, laying these out on the timeline, accounting for all the
constraints and periodicities on the calibrations while trying to minimize
slew times (this is facilitated by the scheduling tool SIRPASS), planning
the downlinks, etc. The provisional schedule is then reviewed by the SSC
Director, Science User Support and instrument scientists. Adjustments are
made, and the schedule is reviewed again by those parties, in addition to the
Observatory Engineering Team and the Mission Manager. After approval, the
timeline is converted into command sequence products and handed over to
the JPL Mission Sequencing Team (MST) for final sequence product
generation and flight rule checking. The scheduling process takes the
better part of 3 weeks with delivery from OPST to MST occurring on the 3rd
Friday.
Sequencing
The JPL Mission Sequence Team uses a set of software tools, called the
Uplink Toolkit, to reformat, constraint check and flight rule check the
products which OPST delivers. There are two passes allocated to this
process, so that problems uncovered on the first attempt can be resolved.
This takes a week and a half for two cycles of processing, review, and
correction. A command conference is then held for final approval of the
sequence and the uplink window begins on the Friday preceeding the
Wednesday on which the sequence begins execution.
Parallel Development Threads
Since it takes 5 weeks of development effort and one week of execution for
each sequence built, there are 7 parallel threads of effort going on at
any one time, with one OPST member assigned to each:
- Week N is executing and being monitored
- Weeks N+1 and N+2 are in the sequencing phase
- Weeks N+3, N+4, and N+5 are in the scheduling phase
- Weeks N+6 and onward are affected by long-range planning updates.
We expect users to monitor the SSC website. An observer
should have 
